1. Field of the Invention
The present invention relates to a cryogenic refrigerator that generates cold by expanding a high-pressure refrigerant gas supplied from a compressor and to a method of controlling the cryogenic refrigerator.
2. Description of the Related Art
A Gifford-McMahon (GM) refrigerator is known as a refrigerator that generates cryogenic temperature. A GM refrigerator changes volume of an expansion space by reciprocating a displacer inside a cylinder. In response to this volume change, the expansion space is selectively connected to a discharge side or an intake side of a compressor, thereby expanding a refrigerant gas in the expansion space.
Such a cryogenic refrigerator includes a compressor for compressing a refrigerant gas and an expander for expanding a refrigerant gas. The refrigerant gas passes through a pipe for circulating a refrigerant gas and circulates between the compressor and the expander. For example, a helium gas is used as the refrigerant gas.
In general, a motor is used as a driving unit of a displacer in an expander of a GM refrigerator. In case of a malfunction of the motor for some reason, a load is applied to components such as the displacer and the like, thereby causing the components to be worn out and replaced earlier. Therefore, early detection of a malfunction of the driving unit is desired.